Poverty is a huge driver of overpopulation. Poor people tend to have more kids to provide for them in their later years. Countries with prosperous economies that are broadly shared tend to have much lower birth rates than poorer countries. That's because raising new humans is a lot of work; if people don't feel like they need to do that, they won't. China, of course, is an exception due to their one-child policy.
And often combined with poor access to contraception, a patriarchy where you want sons to get married not daughters to marry away and a shoddy health care system which means not all your kids might grow up. Even when those things are no longer true it takes time for culture to change and in the meantime you get a huge population bump. That's why we've gone from 2 billion people in 1927 to 7+ billion and counting.